Computer Networks Syed Md. Ashraful Karim Lecturer, CSE BU

Are you able to describe this diagram?

Physical & Logical Topologies Physical topologies –Define the actual layout of the wire (media) Logical topologies –Define how the media is accessed by the hosts

Physical Topologies Bus Ring Star Extended Star Hierarchical Mesh

Physical Topology: Bus Single backbone All hosts directly connected to backbone Each end of the bus must be properly terminated

Physical Topology: Ring No backbone A host is directly connected to each of its neighbors

Physical Topology: Star All devices connected to a central point Center of star is usually a hub or a switch

Physical Topology: Extended Star Connects individual star topologies together. At the center of the star is a hub or a switch. Extends the length and size of the network.

Physical Topology: Hierarchical Like the extended star except a computer controls traffic (not a hub or a switch).

Physical Topology: Mesh Each host has its own connection to every other host. Used in situations where communication must not be interrupted.

Logical Topologies Broadcast Token Passing

Logical Topology: Broadcast Each host on the LAN sends its data (or broadcasts its data) to every other host. First-come, first-serve.

Logical Topology: Token Passing Access to media is controlled by an electronic token. Possession of the token gives the host the right to pass data to its destination.

Technologies Ethernet FDDI Token Ring

Technology: Token Ring Token Ring Token Passing

Technology: FDDI FDDI Token Passing

Technology: Ethernet Ethernet Broadcast

Hosts ComputerServer Printer NIC

LAN Media Symbols Token Ring FDDI Ring Ethernet Line Serial Line

OSI Review: Layer 1 Responsibility: –Transmission of an unstructured bit stream over a physical link between end systems. Concerned: –Bits. –Electrical specifications. –Physical data rate. –Distances. –Physical connector.

LAN Device: Transceiver Connect different media technologies. Layer 1 device. UTP BNC AUI

LAN Device: Repeater Regenerates and repeats the signal. Layer 1 device.

LAN Device: Hub A multi-port repeater. Layer 1 device.

OSI Review: Layer 2 Responsibility: –Provides for the reliable transfer of data cross a physical link. Concerned: –Frames. –Physical address (MAC): Flat. –Line discipline. –Error and flow control. –“Segment”.

LAN Device: NIC Network interface of hosts. Build-in physical address. Layer 2 device.

LAN Device: Bridge Keeps traffic local by filtering traffic based on physical addresses. Layer 2 device.

LAN Device: Switch A multi-port bridge. Layer 2 device.

OSI Review: Layer 3 Responsibility: –Connection and path selection between two end system across networks. Concerned: –Packets. –Logical address: Hierarchical. Networks and Hosts addressing. –Route, Routing table, Routing protocol. –“Network”.

LAN Device: Router Makes decisions based on network addresses (logical addresses). Layer 3 device.

LAN Device: Router Functions Path determination: –The process of evaluating a packet’s destination IP address so that the router can decide which port to send out the packet. Packet switching: –The router re-encapsulates the packet in the protocol needed for the specified port and then switches the packet out that port.

LAN Device: Cloud Another network Include layer 1 – 7 devices

Devices function at Layers